1. Field of the Invention
The present invention relates to a spindle motor of an optical disc player having a self-compensating dynamic balancing apparatus, and more particularly, to an optical disc player having a self-compensating dynamic balancing apparatus capable of compensating for eccentricity of a spindle motor and a turntable to stabilize the spindle motor and the turntable by controlling moving members disposed on a track groove of the turntable to be spaced-apart from each other by a predetermined distance in an initial rotating stage of the spindle motor.
2. Description of the Related Art
Generally, an optical disc player has been widely used due to a high recording density of an optical disc and an advantage of storing data semi-permanently compared with a magnetic tape or other recording media.
The optical disc player includes a laser disc player, a compact disc player, and a digital versatile disc player. Although the compact disc player has been a popular disc player due to a portability and a small-sized volume, the digital versatile disc player is more popular and used than the compact disc player due to a high recording density in the same size as a compact disc.
In the optical disc player, the spindle motor needs to rotate the disc in a high speed without vibration or an eccentric movement of the disc and a turntable. It is very important to stabilize the turntable loaded with the disc to maintain the disc balanced during rotating in the high speed as well as to provide the spindle motor with durability in order to rotate the spindle motor without the vibration and the eccentric movement.
FIG. 1 is a cross-sectional view of a conventional spindle motor of an optical disc player the spindle motor of the optical disc player includes a motor 100 generating a rotation power, a rotating shaft 150 coupled to the motor 100, and a turntable 200 supported by the rotation shaft 150 and loaded with an optical disc D.
The motor 100 includes a plate 110, a burring unit 110′ having a first cylindrical wall protruding upward from the plate, and a holder 120 having a second cylindrical wall with an opening and fitted into a bottom of the first cylindrical wall of the burring unit 110′ through the opening of the burring unit 110′. A metal bearing 130 is forcibly inserted in a space formed between the rotation shaft 150 and the burring unit 110′ and the holder 120. A core 140 having a coil winding around the core 140, to which an external electric power is selectively transmitted, is fixedly attached to an outside circumferential surface of the burring unit 110′. The rotation shaft 150 is rotatably disposed in an central hole of the bearing 130 and supported by the bearing 130 and the plate 110. A thrust washer 160 is coupled to a lower outside end of the rotation shaft 150.
A rotor 170 is coupled to an upper end of the rotation shaft 150 to form an integrated single body with the rotating shaft 150. The rotor has a cap with a cylindrical extension and an opening formed by the cylindrical extension. A cylindrical magnet 180 is coupled to an inside surface of the cylindrical extension of the rotor 170 and spaced apart from the coil of the core 140 to form an air gap with an outside surface of the coil of the core 140.
The rotor 170 having the magnet 180 rotates by an electromagnetic force generated between the coil of the core 140 and the magnet 180 of the rotor 170. The rotation shaft 150 coupled to the rotor 170 and supported by the bearing 130 rotates in response to a rotation of the motor 100.
The turntable 200 rotates together with the rotation shaft 150 of the motor 100 and includes a central protrusion to be inserted into a hole of the optical disc D when the optical disc D is loaded on the turntable 200 and a peripheral portion formed around the central protrusion, extended toward an outside of the central protrusion, and having a flat surface contacting a side of the optical disc D when the optical disc D is loaded on the turntable 200 and clamped by a clamping unit 250.
The turntable 200 includes a main body 210 and a cover plate 220. The main body 210 includes a bottom side of the turntable 200 and a track groove 230 formed on the bottom side of the turntable 200 around the rotation shaft 150 in a circular shape. The track groove 230 includes inner and outer circular guides extended downward from the bottom side of the turntable 200 and spaced apart from each other by a distance to form an opening. A plurality of balls 240 are movably and rotatably disposed within the track groove 230 and between the inner and outer circular guides. The cover plate 220 is coupled to the inner and outer circular guides to cover the opening of the track groove 230 while the balls are disposed in the track groove 230. The balls are disposed on the cover plate 220 and spaced apart from the bottom side of the turntable 200 by a predetermined height.
When the turntable 200 rotate together with the optical disc D in the high speed after the optical disc D is loaded and clamped on the turntable 200, the balls moves along the track groove 230 at a compensating position on the track groove 230 of the turntable 200 opposite to an eccentric position of an eccentric force in the turntable 200 with respect to a center of the rotation shaft 150. The movement of the balls to the compensating position compensates for eccentricity of the turntable 200 by generating a counter-centrifugal force and a bounding force. Thus, the vibration and the eccentric movement of the turntable 200 are prevented
Since the balls 240, which are rotatably disposed in the track groove 230 move toward the compensating position within an initial rotation stage (period) before an initial speed of the turntable 200 and the motor 100 is changed to a normal (high) speed of the motor 100, the counter-centrifugal force is generated in response to the eccentric force of the turntable 200.
The eccentric force of the turntable 200 must be compensated within the initial rotation period before the motor rotates in the normal high speed in the optical disc player. However, the balls 240 are irregularly or non-uniformly arranged in the track groove 230 when the motor and the turntable do not rotate but are in a stationary state. In this state, the balls 240 cannot move to the compensating position from an irregular position when the motor 100 rotates, and the eccentricity of the turntable 200 cannot be compensated.
That is, the balls 240 disposed in the track groove 230 of the turntable 200 of the spindle motor in the optical disc player are not arranged regularly and uniformly in a predetermined distance and a predetermined position but irregularly and non-uniformly arranged due to friction between the balls 240 or between the track groove 230 and the balls 240 as shown in FIG. 2. If the motor 100 rotates, the balls 240, which are disposed irregularly in the track groove 230, rotates along the track groove 230 by the centrifugal force and the friction occurring due to a rotational force of the motor 100. Thus, the balls 240 do not move to a counter-centrifugal force position p1 for compensating for an actual eccentric mass me1 but move to an incorrect counter-centrifugal force position p2 to compensate for the incorrect eccentric force me2. If the incorrect counter-centrifugal force is generated in the incorrect counter-centrifugal force position p2, the incorrect counter-centrifugal force is compensated but the actual eccentric force cannot be compensated. As a result, the vibration and noise are generated from the motor 100 and the turntable 200, and a driving characteristic of the motor 100 is lowered.